Topology aware MANET for mobile networks

ABSTRACT

Systems and methods provide adaptability in a mobile ad hoc network (MANET), based on an existing protocol, such as adaptive hybrid domain routing (AHDR). The systems and methods are especially suited for fast changing topologies that may change after a reactive route discovery has been completed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 14/037,697filed Sep. 26, 2013 which was divisional of U.S. application Ser. No.13/069,808 filed Mar. 23, 2011 which was a divisional of U.S.application Ser. No. 11/897,474 filed Aug. 30, 2007 now U.S. Pat. No.7,936,697 issued May 3, 2011, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed generally to improvements in wirelesscommunication networks. More specifically, the present invention isdirected to mobile ad hoc networks and related methods.

BACKGROUND OF THE INVENTION

Wireless networks have experienced increased development in the pastdecade. One of the most rapidly developing areas is mobile ad hocnetworks (MANETs). Mobile ad hoc networks or MANETs are self configuringnetworks in which a number of mobile nodes may interconnect with oneanother via wireless links. The locations of the nodes with respect toone another, i.e., the topology of the network, may therefore changerapidly particularly when such networks are deployed in emergencysituations or in military operations.

Physically, a MANET includes a number of geographically distributed,potentially mobile nodes sharing one or more common radio channels.Compared with other types of networks, such as cellular networks orsatellite networks, the most distinctive feature of MANETS is the lackof any fixed infrastructure. The network is formed of mobile (andpotentially stationary) nodes, and is created on the fly as the nodescommunicate with each other. In this type of network, the routing nodesare allowed to move and form a dynamic autonomous network with anarbitrary topology. The network does not depend on a particular node anddynamically adjusts as some nodes join or others leave the network. AMANET is also referred to as a “multi-hop network” because multiplewireless transmission hops may be necessary to forward message packetsbetween nodes in the network.

In a military joint airborne environment, efficient networking requiresoperational flexibility with ad-hoc management of networking resources.It is also important to maintain low overhead so that bandwidth remainsavailable for communication among users. Network users may also requireend-to-end quality-of-service (QoS) support to manage latency,stability, and response time. Other desirable operational requirementsmay include security, adaptability, interoperability, speedy join time,and rapid network formation.

MANETs are attractive because they provide instant network formationwithout the need for connection planning and routing nodeadministration. The result is ease of deployment, speed of deployment,and decreased dependence on a fixed infrastructure. Despite theiradvantages, however, MANETs must overcome numerous obstacles toeffective communications. As such, there are a number of issues withMANET that need to be addressed.

One issue is network management. An implicit assumption within a MANETis that every node within the network may wish to communicate with everyother node within the network. The MANET protocol defines all nodes asrouters, and then goes about trying to comprehend how each routermaintains real time knowledge about the existence of other routerswithin the network. This becomes an exponential task to manage as thenetwork increases in size. This problem is compounded by the ability ofthe nodes to dynamically enter or leave the network in an “ad hoc”fashion. The ad hoc nature of the network creates an onerous networkmanagement problem, flooding the network with status packages requiringconstant updates.

Another issue is bandwidth. As nodes enter, leave, and move around theMANET, the MANET is constantly changing. Requiring each node in theMANET to be aware of changes made by the entry, departure, or movementof a node would consume a great deal of the available bandwidth.

Another issue is power. Mobile computing systems typically rely onbattery power. Since battery power is limited and communicating withinthe network is power-intensive, having each node update itself asanother node enters, leaves, or moves with the MANET may consume a largepercentage of the available power.

Another issue is complexity. As the number of nodes in the MANETincreases, the number of routes through the MANET increasesexponentially. For even a relatively small number of nodes (100 istypically considered a sizeable MANET), the time required to update arouting table for the MANET may take longer until another node enters,leaves, or moves within the MANET. In addition, the space requirementsfor storing the routing table may quickly exceed the available space inthe node.

Another issue is frequency usage. The mobile nodes in a network mustshare common radio frequencies and are therefore prone to greaterinterference from each neighboring node. All functions have to bedistributed among the nodes. The distance between two nodes oftenexceeds the radio transmission range, and a transmission may have to berelayed by other nodes before reaching its destination. Consequently, aMANET network typically has a multi-hop topology, and this topologychanges as the nodes move around.

Another issue is rapidly changing topologies. Analysis of existing MANETprotocols show a need for enhancements in a mobile environment withrapidly changing topology.

The present invention addresses the foregoing needs.

SUMMARY OF THE INVENTION

The present invention provides systems and methods directed to providingadaptability in a mobile ad hoc network (MANET), based on an existingprotocol, such as Adaptive Hybrid Domain Routing (AHDR), outlined inpreviously filed application Ser. No. 11/546,783, incorporated byreference herein in its entirety. The systems and methods are especiallysuited for fast changing topologies that may change after a reactiveroute discovery has been completed.

According to one embodiment, a method is provided which adaptivelyrefreshes hop k routes and upkeeps these routes only if needed, therebypreventing dissemination of stale data and also reducing controloverhead in the network.

According to another embodiment, a method is provided based on adistributed update rate optimization and domain lead and bridge nodeselection algorithms, optimized on the relative mobility of each node toits neighbors.

According to yet another embodiment, a method is provided based on anefficient algorithm for providing route persistence based on a reactiveroute discovery technique which eliminates stale route resolutions.According to this embodiment, the technique employs a timer controlbased on topology changes to prevent route staleness.

For a better understanding of the invention, reference is made to thefollowing description taken in conjunction with the accompanying drawingand the appended claims.

DESCRIPTION OF THE DRAWING FIGURES

These and other objects, features and advantages of the invention willbe apparent from a consideration of the following Detailed DescriptionOf The Invention considered in conjunction with the drawing Figures, inwhich:

FIG. 1 is a diagram of an exemplary ad hoc network with multipledomains;

FIG. 2 is a diagram of an exemplary ad hoc network with selected domainlead and bridge nodes;

FIG. 3 is a diagram of an exemplary network including a fast movingcluster and a slow moving cluster;

FIG. 4 is a diagram of an ad hoc network illustrating adaptive routediscovery in a fast moving topology;

FIG. 5 is a diagram of an ad hoc network illustrating adaptive handoffin a changing topology; and

FIG. 6 is a diagram of an ad hoc network illustrating a collection ofmultiple paths and link performance metric in a mobile ad hoc network.

DEFINITIONS

The following definitions apply to terms used herein to describe theinventive AHDR protocol.

Link State Level (LSL): A rating of, e.g., zero to 15, representing thestate (e.g. quality and/or congestion) of a transmission link for agiven entry in a node's H1 or H2 table. LSL may be determined from LinkQuality and Link Congestion.

Domain Lead (DL) Node: A node having the most coverage of its 1 hopneighbor nodes. The DL node may send a TU1 message periodically andexchange network topology information with DL nodes of other domainsless frequently in the form of topology update domain (TUd) messages. Anode announces its DL status via a domain lead announcement (DLA)message to its neighbors. The former DL node renounces its DL status bybroadcasting a domain lead renouncement (DLR) message to its neighbors.

Domain Node: A node that is a member of a domain with at least one DLnode within 1 hop range of itself. A domain node may broadcast a TU1message periodically, and is able to issue Route Discovery (RDisc)messages and receive Route Resolution (RRes) messages as defined below.

Domain: The region surrounding a DL node and containing all domain nodeswithin 1 hop distance from the DL node. That is, a DL node can reach allnodes contained within its domain via 1 hop, and vice versa.

Bridge Node: A node belonging to a set of one or more nodes that areselected by a domain node (including a DL node). A bridge node acts tobridge a domain node that selected it with nodes in other domains of thenetwork. Bridge nodes are selected strategically to maximize a domainnodes ability to reach nodes in the other domains with minimal controloverhead while providing the highest coverage of neighboring domains.

Link Node: An intermediate node which is the next hop from a node thatis originating or forwarding a message along a route to another node inthe network.

Hop 1 Topology Update (TU1): A message exchanged among all domain nodescontaining the ID of originating node, the node's 1 hop neighbors, andthe DL of the originating node's domain.

Topology Update Domain (TUd): A message exchanged among DL nodesthroughout the network to disseminate information concerning nodescontained in the DL node's respective domains.

Route Discovery (RDisc): A message transmitted by a domain node wishingto obtain a route to a desired destination node.

Route Resolution (RRes): A message addressed to a domain node after aroute to the desired destination node is resolved, in response to aRDisc Message from the domain node.

Network Entry: An event that occurs once a node obtains informationconcerning neighboring nodes, and is able to reach all other nodes inthe network on demand, i.e., the entering node has identified a DL nodewithin 1 hop.

Update Rate (Tf): Rate at which a given node sends control messages andupdates routing tables.

Timer: Indicator in routing table on route persistence for a given linkto neighbor nodes. The timer is decremented periodically (depending onupdate rate) and neighbors are removed from the routing tables when thetimer runs out.

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set firth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime and multiple primenotations are used to indicate similar elements in alternateembodiments.

The detailed description is divided into eight sections. In the firstsection, a general overview is described. In the second section, asystem level overview is described. In the third section, domain leadand bridge node selection is described with regard to their adaptiveselection in view of a fast changing topology. In the fourth section,the link stability metric is described with regard to an adaptivecalculation component. In the fifth section, adaptive update rate androute persistence is discussed in relation to adaptively calculatingeach value. In the sixth section, alternate route discovery is discussedin relation to its performance being adaptive to a fast changingtopology. In the seventh section, adaptive routing and handoff isdiscussed. Finally, in the eighth section, multiple paths available foradaptive technologies is discussed.

1. General Overview

The present invention concerns a network message routing protocol foruse in mobile ad hoc networks (MANETs), especially MANETs deployed intactical environments wherein the node topology of the network maychange rapidly. Referred to herein as Adaptive Hybrid Domain Routing(AHDR).

In a manner that is greatly simplified, but sufficient for understandingthe invention, an ad hoc network can be thought of as a set or one ormore groups of nodes with routing capability that may be fixed ormobile. At its most general, a mobile ad hoc network or MANET isdescribed that employs (AHDR) routing protocol. The AHDR routingprotocol embodies certain enhancements for highly mobile environmentsand fast changing topologies, such as, for example, increased networkcapacity and bandwidth resolution methods. These enhancementsadvantageously increase network capacity, reachability, and networkavailability, as will be described.

The AHDR protocol described herein implements a strategic hybridcombination of proactive and reactive schemes, which provides updatedroute information for neighbor nodes, and offers optimized routeresolution for unknown routes in a fast changing topology. The AHDRnetwork is composed of domains (which may overlap) and each domain hasone designated Domain Lead (DL). The proactive component of AHDR updatesrouting information within each domain regularly, and DLs exchangedomain information throughout the entire network. To reduce the overheadassociated with the control and management of an ad hoc network, therate of information exchange within each domain and across domains isadaptive to topological and configuration changes in addition tooperational and QoS needs. The set of optimization parameters forrouting decision is configurable via the network management.

The reactive component of AHDR quickly obtains route information ondemand for new destinations not already available, e.g. routeinformation for a new node entering in one part of a large network isnot yet propagated to another part of the network. AHDR usesmulticasting through bridge nodes to efficiently propagate updates andqueries throughout the network. Each node selects a set of bridge nodesthat provides maximum logical reach within one hop, and offersdirectional routing information from which the entire network can bereached. In the case of a large, densely populated area with frequentlychanging topology, AHDR offers an advantage with a priori directionalinformation of the destination, and efficient destination resolution forunknown routes. With proactive routing within a designated range wheremost traffic exchange takes place, the connection establishment time canbe reduced. Furthermore, reactive routing reduces the amount of controltraffic by discovering the path on demand for destinations outside theimmediate neighboring nodes.

2. System Level Overview

As shown diagrammatically in FIG. 1, a multicast ad hoc network 100 maybe considered as comprising multiple domains, which may overlap. Eachdomain (D₁₋₅) includes one designated domain lead (i.e., DL₁₋₅).

Generally, in a network having a multicast proactive routing protocol,each router knows the topology of the network, so it is capable ofdetermining the shortest (or optimum) routing path for conveying data tothe source router RS.

Referring to FIG. 1, an exemplary multicast ad hoc network 100 is shownbeing comprised of multiple domains, which may overlap. Each domain(D₁₋₅) includes one designated domain lead (i.e., DL₁, DL₂, DL₃, DL₄,DL₅, DL₆). Each domain further includes some number of bridge nodes BNfor linking a given domain node to nodes in corresponding neighboringdomains. For example, two bridge nodes link domain lead DL₁ to nodes incorresponding neighboring domains (e.g., domains 2 and 3).

3—Adaptivity of Domain Lead (DL) and Bridge Node (BN) Selection

Domain Lead (DL) and Bridge Node (BN) selection accounts forneighborhood connectivity status. This is adaptive to the state of thetopology and allows for smooth handoff between DL and BN transitions.

Domain Lead Adaptivity

Domain Leads (DLs) are selected mainly on the basis of Node Coverage(NC), which can be expressed in terms of a weighted function derivedfrom the number of hop 1 nodes within range and their corresponding LSLvalues. See equation 1 below. Every node in the network calculates itsown node coverage (NC), as well as its neighbors. When a node has thelocal maximum NC with stable routes, it will be designated the DL ofthat domain.

The node coverage (NC) of a node, e.g., node A, can be calculatedaccording to the following formula.NC(A)=s ₀ *[w ₀ *n+(w ₁ *s ₁ +w ₂ *s ₂ +w ₃ *s ₃ + . . . +w _(n) *s_(n))]  Eq.[1]Where

s₀=state of node A

n=the total number of nodes within 1 hop around A

w₀=adaptive weight put on number of nodes

w₁ . . . w_(n)=weights of each neighbor node depending on state and LSLw _(n)=(LSL*min(1,max(0,LSL−a)))+(z*max(0,(LSL−(15−b))))

-   -   where    -   a=: sets how many of the bottom LSLs get zeroed.    -   b=: sets how many of the top LSLs get scaled up    -   z=weight of higher LSL

s₁ . . . s_(n)=state of each neighbor node

-   -   higher weight for free node than domain node and DL    -   With default values, z=3, a=1, and b=3, we get the following        weights for w_(n):

Neighbor Node 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 LSL 0 1 2 3 4 5 6 78 9 10 11 12 13 14 15 Weight 0 0 0 0 4 5 6 7 8 9 10 11 12 14 16 18

It should be noted that low mobility nodes tend to have a highers-weight than relatively mobile nodes. Higher stability correlates to ahigher s-weight, in terms of topology change, link variations, etc. Alsofree nodes have a higher s-weight than domain nodes.

As discussed above, to reduce the overhead associated with the controland management of the network, the rate of information exchange withineach domain and across domains is adaptive to topological andconfiguration changes in addition to operational and QoS needs. Inaddition these changes, the weights W on each network node may be madeadaptive with respect to various factors including, expected mobility,stability, link performance.

As illustrated in equation [1] above, the node coverage, NC, is afunction of s₀, the state of a node, e.g., node A. The state of a node,s₀, is in turn dependent upon three things, free nodes, low mobility andhigh stability. Each factor is described as follows.

To make the state of a node s₀ adaptive to mobility, a link changethreshold percentage, Y % is established, during system configuration. Asecond parameter, X, representing a threshold delta LSL increment valueis also established during system configuration.

In operation, at each update increment, e.g., 2Tf, a node determineswhat percentage, e.g., Z %, of links have changed by more than X LSLincrements, where X is a positive integer and Z is a value between 1 and100. If the percentage Z % of link changes, in excess of X LSLincrements, exceeds Y %, the pre-established threshold percentage, thestate of a node s₀ is adjusted downward to reflect a high mobility node,which is reflected in the calculation of NC (see equation 1). S₀, thestate of a node, incremented and decremented at a predefined levels,such that s₀ stays within a given range, e.g. between 1 and 3.

Free nodes have a higher base s0 value, e.g. they start with s0=2instead of 1. If 2 nodes see the exact same number of nodes with thesame LSL values, but one sees a free node, the node that sees the freenode would have a higher NC because the free node would have a higher s0which contributes more to the NC. Similarly, if the node itself is afree node, it will have a higher multiplicative s0 value by which itsentire NC value is scaled by. More often than not, a free node willdesignate itself DL to refrain from disrupting an existing stabledomain.

It should be understood that for fast moving networks, the thresholdpercentage Y % of link changes may selected to be a larger value thanfor a slow moving network.

Bridge Node Adaptivity

Each node, including the DL node, selects its own set of Bridge Nodes(BNs) for TUd dissemination and inter-domain information exchange. BNselection is also adaptive to network coverage of each node, derivedfrom the Neighbor Domain Coverage (NDC) of its H1 neighbors, with theexception of DLs within range.

Each node (including DL) will select its own set of BN for TUddissemination and inter-domain information exchange. BN selection isalso adaptive to network coverage of each node, derived from theNeighbor Domain Coverage (NDC) of its H1 neighbors, with the exceptionof DLs within range.

Selecting a bridge node (BN) that has the most Neighboring DomainCoverage (NDC) will allow more efficient propagation of TUd messagesthrough domain nodes. Each node will also take into account the linkstability metric of potential BNs with high NDC. In the case of highmobility, the stability metric will have higher weight in the BNselection algorithm. Please see Section (2) for Stability metric.

A node will be selected as a bridge node if it has the highest NDC forone or more neighboring DL ID.

Neighboring domain coverage (NDC) is computed from a similar weightedfunction that normal H1 NC is derived from. H1 data exchange mustinclude the NDC of each neighboring domain, along with the DL of thecorresponding NDC.

In the computation of NDC for a bridge node, the NDC weights are adaptedin a similar manner to that described above for equation 1.

Because the NC calculation includes all 1 hop neighbors, the sum of allNDCs of a node should equal NC.

NDC for node A:

${{\sum\limits_{i = 1}^{n}{NDC}_{i}} = {NC}},{{{where}\mspace{14mu} n} = {{total}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{{domains}.}}}$

The neighboring domain coverage (NDC) of a node A for Domain I, may becomputed as follows:NDC(A,i)=s ₀ *[w ₀ *n+(w ₁ *s ₁ +w ₂ *s ₂ +w ₃ *s ₃ + . . . +w _(n) *s_(n))],  Eq. [2]Similarly, where:

s₀=state of node A

n=the total number of H1 nodes that claims DLi as its DL

w₀=adaptive weight put on number of nodes

w₁ . . . w_(m)=weights of each neighbor node depending on state and LSLw _(n)=(LSL*min(1,max(0,LSL−a)))+(z*max(0,(LSL−(15−b))))

-   -   a=: sets how many of the bottom LSLs get zeroed.    -   b=sets how many of the top LSLs get scaled up    -   z=weight of higher LSL

s₁ . . . s_(n)=state of each neighbor node

If two nodes have equal NDC to a certain domain, the node with thehigher stability is selected. A higher Link Stability Indicator (LSI)metric reflects lower mobility. The next section describes LSI in moredetail.

4—Link Stability Metric

While a link may exhibit stability at any instant in time, it does notguarantee that the link has been stable in the past. For example, a linkthat currently appears to be stable may have been extremely unstableonly a short time ago in the past (e.g., 2 seconds ago). Similarly, thesame link may experience periods of stability and instability over time.It is therefore desirable to derive a metric which provides some insightregarding a link's stability over time to handle scenarios in whichinelastic traffic needs to be reliably transmitted over the network. Forexample, it is desirable to know the weighted average link quality for agiven amount of time to ensure quality of service requirements.

For these situations, where consistent quality of a link becomes anissue, it is contemplated to compute a link stability metric (LSI) as aquantitative measure of a link's reliability. The LSI metric, accordingto one embodiment, relies on a moving weighted average of presentlyacquired system metrics, such as LCI and LQI, which are fundamentalmetrics collected in the normal course of system operation. The LSImetric is contemplated for use as a general predictor of a link'sreliability in the future. While, it is acknowledged that the past isnot a perfect predictor for future stability, the LSI metric provides aneasily derived and dependable metric for predicting future performancewithout incurring substantial additional overhead.

As is well known, the two fundamental metrics for determining thestrength of a link are congestion and quality. These metrics arecombined into the Link Stability Indicator (LSI) metric, based on amoving weighted average of previous changes to a link, which isespecially useful in measuring the reliability (i.e., stability) of alink in the presence of mobility, as will be described.

The link stability (LSI) metric for a given node provides information onthe mobility of the node in relation to the rest of the network. Inaddition to computing LSI for particular nodes in a network, it iscontemplated to compute a domain link stability metric for each domainthat will help configure the adaptive update rate for that domain. Linkstability as it relates to the adaptive update rate is discussed in thenext section, section 5, below. Briefly, a fast moving node may want tosend out more frequent periodic updates, but a fast moving node that isnot receiving or transmitting should not clutter the system withoverhead.

Referring now to the computation of the Link Stability Indicator (LSI)metric, the fundamental (i.e., atomic) metrics, LCI and LQI, which arequantitative measures of congestion and quality, respectively, arecombined to calculate the link stability metric, i.e., the linkstability indicator LSi_(ij), at time t such that negative LQI trendsreduce the indicator slightly faster than positive trends improve it, aswill be described below.

It is appreciated that the Link Stability Indicator (LSI) metric iscalculated, in a preferred embodiment, as a weighted moving averagetaking into account past values of LCI, LQI and LSI.

To calculate a link stability metric between two nodes, (e.g. nodes iand j), the following general equation is applicable.

A general expression for Link Stability may be generally stated asfollows. It is shown to be a function of LCI, LQI and mobility:LSI_(ij)(t)=(w ₁ΔLCI_(WMA)(t),w ₂ΔLQI_(WMA)(t),w ₃ m _(i) ,w ₄ m_(j))  Eq. [3]Where:

-   -   ΔLCI_(WMA)(t)—Weighted moving average of ΔLCI    -   ΔLQI_(WMA)(t)—Weighted moving average of ΔLQI    -   m_(i)=mobility₁=(#1's good link)/(#1's link changes

As illustrated in equation (3), Link stability is a function of LCI, LQIand mobility where mobility is calculated as a ratio of good links tolink changes. Link changes are computed in accordance with the followingequation:LSL change>N in X[TF]  Eq. [4]

Equation (4) states that for a given link i, at every update period orinterval X, for those links in link I's routing table, a link change issaid to occur whenever the change in LSL of a link is greater than N,where N is a pre-determined threshold.

Table I illustrates, by way of example, how a link's stability (e.g.,link i) may be characterized in accordance with its mobility. As shown,stable links are characterized as having lower mobility.

TABLE I # changes # good mobility Mobile 8 10 4/5 Moderate 10 18 5/9Stable 2 18 1/9

Referring again to equation (3), the term, ΔLCI_(WMA)(t), represents aweighted moving average of LCI over time. The weighting scheme may bedifferent in different embodiments. In one exemplary embodiment, asillustrated below in equation (4), the weighting scheme utilizes a setof constant weights {4, 3, 2, 1} taking into account the four mostrecently acquired values of LCI, which are biased in favor of the morerecently acquired values. It should be understood, however, that thereare no restrictions the quantity or type of weight terms used. Anyweighting scheme is within contemplation of the invention.

$\begin{matrix}{{\Delta\;{{LCI}_{WMA}(t)}} = \frac{\sum\limits_{i}^{n}{( {n - i} )\Delta\;{LCI}_{i}}}{2n}} & {{Eq}.\mspace{14mu}\lbrack 5\rbrack}\end{matrix}$Where n=number of updates stored, and i=1 is most recent t, i=2 is t−1,etc.

A similar computation is performed to derive a weighted moving averagefor ΔLQI_(WMA)(t)

By default, the Adaptive Hybrid Domain Routing protocol, AHDR, retainsthe last 5 LCI and LQI values for each link, thus n=5 for ΔLCI/ΔLQI WMAvalues derived from LCI/LQI.

For example:

$\begin{matrix}{{\Delta\;{{LCI}_{WMA}(t)}} = \frac{{4\Delta\;{LCI}_{t}} + {3\Delta\;{LCI}_{t - 1}} + {2\Delta\;{LCI}_{t - 2}} + {\Delta\;{LCI}_{t - 3}}}{10}} & {{Eq}.\mspace{14mu}\lbrack 6\rbrack}\end{matrix}$

The link stability metric may be further enhanced to not only accountfor LCI, LQI and mobility but may also take into account weighted pastvalues of LSI, as shown in equation [6]. Further, as shown in equation(6), the fourth term multiplies the ΔLQI by a factor of 1.2 in the casewhere the ΔLQI is getting better and by another factor of 2 in the casewhere the ΔLQI is getting worse. In this manner, the link stabilitymetric is more sensitive to negative changes in ΔLQI. In other words,drops in link quality are emphasized more strongly than improvements inlink quality.

$\begin{matrix}{{{LSI}_{ij}(t)} = {{\Delta\;{LQI}_{WMA}} + {\Delta\;{LCI}_{WMA}} + {\alpha\;{{LSI}_{ij}( {t - 1} )}} + \{ \begin{matrix}{{\Delta\;{LQI}_{t}} > 0} & {\beta_{1}( {\Delta\;{LQI}_{t}} )} \\{{\Delta\;{LQI}_{t}} \leq 0} & {\beta_{2}( {\Delta\;{LQI}_{t}} )}\end{matrix} }} & {{Eq}.\mspace{14mu}\lbrack 7\rbrack}\end{matrix}$

It is noted that equation (6) does not accounting for mobility. Themobility factor is accounted for in equation (7), belowLSI_(ij)(t)=(1−m _(i))(1−m _(j))LSI′_(ij)(t),m≦1  Eq. [8]

If the node is extremely mobile and there are more link changes thangood links, then (1−m) may be negative, thus has a floor value of zero.This equation takes into account both the mobility of node i and j, andscales LSI′ accordingly to capture respective node mobility.

Providing a link stability metric serves to enhance route and next hopselection by not choosing routes and next hops that contain a link witha “small” link breakage timer. The ability to identify and use stableroutes minimizes the disruption caused by mobility.

In addition, the link breakage timer can be used to influence the TU1,and TUd update frequency. This way the fixed TUx timer based updated canbe dynamically adapted and frequent updates may not be necessary savingrouting control overhead because routes are established based on linkstability.

5—Adaptive Update Rate and Route Persistence

AHDR adapts to the state of the network by continuously tuning theupdate rate of each node based on relative mobility measured by routingtable changes over time. Distributed update rate optimization measuresrelative mobility of each node to its neighbors and determines theoptimal update rate for each node. Adaptive timer control for routepersistence and adaptive update rates accommodate fast changingtopologies. Since the adaptive measures are derived from routing tablechanges over a given period of time, a single fast mover will not impactthe update rates of the rest of the network.

A full update is sent every N updates. For those updates performed inbetween, the update only includes changes in the routing tables thatexceed a certain pre-defined threshold. This results in a savings inoverhead by updating only those links that have experienced a notablechange (i.e., exceeding the threshold). The threshold may be determinedby QoS requirements.

In a fast changing topology, the route persistence of a given linkexisting between two nodes that is quickly degrading should not be thesame as the route persistence of a stable high quality link. Adaptivetimers are applied to links that are very low quality (e.g. LSL<3) orlinks that change more than a certain threshold in a given amount time.If the link is weak or the threshold is surpassed, then the timer of thelink is reduced to a lower number. This prevents weak links fromremaining in the routing tables after they are no longer available, butat the same time, keeps more stable links around if an update was lostdue to interference or collisions.

Referring now to FIG. 3, a group of nodes in a fast moving cluster 24are moving at a much higher velocity than the other slower moving orstationary nodes and consequently experience a higher number of routechanges in their respective routing tables. This fast moving cluster 24of nodes will send updates at a faster rate, to prevent staleinformation from the rest of the network. As other slower moving cluster22 of nodes receive the updates from the fast moving cluster 24 ofnodes, the other slower moving nodes update their timer and routingtables at the rate at which each node designates in their routing updatemessages. Each node will include its update rate in its TU1 messages, soevery other node can know when to expect TU1 messages from every othernode. It should be understood that TU1 messages comprise both full TU1messages and delta TU1 messages.

6. Alternate Route Discovery (Adaptive to Fast Changing Topology)

Referring now to FIG. 4, there is shown a diagram of an ad hoc networkillustrating adaptive route discovery in a fast moving topology. AHDRissues a Route Discovery (RDisc) message from node S to node D, and aroute was created between the two nodes and an entry is created in therouting table for this link. After the original data flow has completed,another application from S requests another session with D. But sincethen, bridge node BN4 has moved out of 2 hop range of bridge node BN3.In accordance with invention principles, and Alternate Route Discovery(ARdisc) from S to D will not generate ARRes until D has been located inthe hop2 table.

A Route Discovery (RDisc) approach that does not accommodate fastchanging topologies is described in co-pending U.S. patent applicationSer. No. 11/546,783, incorporated by reference in its entirety herein.The method is briefly described herein as follows.

When a source node wants to send a message to a known destination node,it first searches its routing tables for the desired node. If thedestination node is beyond 2 hops and no route can be determined fromthe current table entries, then the source node relies on the reactivecomponent of AHDR in which the domain lead and the bridge nodes have arole. Specifically, the source node generates a Route Discovery (RDisc)message and sends it to the DL node. The source node then waits for aRoute Resolution (RRes) reply message from the DL node. When the DL nodereceives the RDisc message, it acts as follows. If the DL node canlocate the destination node within its own muting tables (H1, H2, orHk), it generates a RRes message for the source node. The RRes messagespecifies, inter alia, a target node with which the source node can linkin order to reach the destination node. If the DL node cannot locate thedestination node in its own routing tables, it forwards the RDiscmessage to the DL node□s selected bridge nodes. When the bridge nodesreceive the RDisc message from the DL node, they act as follows. If a BNcan locate the destination node within its own routing tables, itgenerates a RRes message and transmits it to the LastID (i.e., the DLnode that forwarded the RDisc message). The bridge node also forwardsthe RDisc message to the destination node. If the BN cannot locate thedestination node within its routing tables, it forwards the RDiscmessage to all domain lead nodes within 2 hops, unless such a DL nodewas the LastID of the received message, or is already listed in theRDise message.

The method described above may be modified in accordance with thepresently described embodiment to account for fast changing topologies,to be described as follows.

A source node generates an Alternate Route Discovery (ARDisc) message inthe same manner as the (RDisc) message is sent, as described above.Previously, if the DL node can locate the destination node within itsown routing tables (H1, H2, or Hk), it generated a RRes message for thesource node. Instead of sending an RRes message, as described above, anARRes message is generated to be sent to the source node. A keydifference between the ARRes message and the Rres message is that theARRes message will not be sent until the destination node is actuallylocated in the H2 table. In this way, it is guaranteed that thedestination node is seen within 2 hops before a reply is generated. As aresult of not sending the ARRes message until the destination node isactually located in the H2 table, an non-updated (i.e., stale) Hk entryis prevented from triggering a Rres message and stale route resolutionsare eliminated. Both of these consequences are effective in dynamicnetworks. In essence, no trust is placed in neighboring information,located in a node's Hk table, when generating route resolution messages.

7—Adaptive Routing and Handoff

AHDR implements a method of signaling lower layers of link changes in amobile environment. In the time it takes for a packet to enter the queueand for the packet to be transmitted, the topology may have changed.Similarly, in a rapidly changing topology, links may fade in and outwith mobility.

In one embodiment, a method is provided to handle the triggering betweenAHDR and other layers to signal link changes and adaptive handoff of aflow.

Every node in the network is responsible for distributing its own localinformation, and each node has the most knowledge of the fast changingtopology directly around it. AHDR routes on a per hop basis, giving eachnode the ability to make the next hop decision depending on the linkperformance of the route. Multiple routes are stored in the routingtables for each destination node, so the next hop routing decision ismade at each hop. As a result, if a link state becomes congested, thecurrent link node can reroute a packet stream through an alternativenext hoop neighbor node without the overhead associated with informingthe source node of such route changes.

Referring now to FIG. 5, there is shown an ad hoc network illustratingadaptive handoff in a changing topology. An original path between nodesS and D was through LN1 and LN3. However, as the link quality betweenLN1 and LN3 may become diminished due to any number of factors,including, for example, rapid congestion, fading, interference, topologychanges or combinations thereof. LN1 link observer tracks the routestate and redirects packets to LN2 in real time. Source node S continuesto send packets to LN1 and is not concerned with the routing decisionsbeyond the next hop, while from the perspective of node D, the messagestream is uninterrupted.

As continuous dataflow persists between 2 nodes, the sender isconstantly evaluating the LSL of the link. When the LSL drops below acertain threshold designated by QoS, then the node will automaticallyselect a better next hop neighbor for the flow.

8—Multiple Paths Available for Adaptive Topologies

AHDR collects multiple paths between source and destination, thusproviding QoS routing support for various QoS routing requirements.These multiple paths enable collection of various QoS metrics, whichdetermine the types of QoS that the network can support. Different pathswill be selected for traffic of different QoS transport requirements.For example, a path selection algorithm for traffic with end-to-endtransport delay requirements needs to take into account the path delaymetric in addition to other path metrics while the algorithm forbandwidth sensitive traffic does not.

In one embodiment, AHDR is integrated with a QoS routing solution thatimplements a path selection algorithm.

As discussed in co-pending application Ser. No. 11/546,783, the LinkState Level (LSL) for a one hop (H1) neighbor node may be measured andassigned by the network's MAC layer when the local node receives a TU1message from the H1 node. The LSL may be defined by two factors; namely,a Link Quality Indicator (LQI) and a Link Congestion Indicator (LCI).Each factor may have, e.g., four levels; the higher the level, thebetter the transmission condition.

LQI may be calculated from, e.g., bit error rate, packet error rate,erasures count, acknowledged frames, and CRC error count. LCI may becalculated from, e.g., bits-per-second, packets-per-second, bit count,and packet count.

The overall LSL may then be represented at, for example, 16 levels asshown in the table:

L4 L3 L2 L1 (3) (2) (1) (0) L4 (3) 15 13 10 6 L3 (2) 14 11 7 3 L2 (1) 128 4 1 L1 (0) 9 5 2 0

Referring now to FIG. 6, when a Tud is sent between DL1 and DL6, LP, thetotal link performance is collected via every path. As previouslydescribed in copending application Ser. No. 11/546,783, LP is the totallink performance of the route to the hop 2 node, taken from the lower ofthe LSL_(1k) and LSL_(2k) values.LP=(LSL_(hop1)+LSL_(hop2)),MIN(LSL_(hop1)+LSL_(hop2))

AHDR provides QoS information to determine the appropriate path for agiven application or packet for transmission. As the topology changes,AHDR adaptively provides updated LP for the paths. AHDR provides thefollowing Link Performance metric that allows adaptive path selectionfor various QoS requirements.

In one embodiment, one exemplary Link Performance metric, the LCI andLQI count are both one byte values, each split into four (4) levels.

LCI/LQI values of [0,1], [2,3], [4,5], [6,7]

The LCI and LQI count parameter lengths are configurable depending onnetwork characteristics. For example, in one embodiment, each of thecount parameter lengths may be 2 bytes each.

The LCI and LQI are calculated at each hop, and depending on each value,the corresponding LP bit fields are incremented. In the example below,LCI and LQI metrics are 2 bit values, mapped to corresponding LinkPerformance counter bits. LP counter bits are 2 bit fields for eachLCI/LQI value level, and the LP counter bits are incremented at each hopdepending on LCI/LQI of that link.

Level LP counter bits LCI value 1 [0, 1] [0, 1] 2 [2, 3] [2, 3] 3 [4, 5][4, 5] 4 [6, 7] [6, 7] LQI value 1 [0, 1] [8, 9] 2 [2, 3] [10, 11] 3 [4,5] [12, 13] 4 [6, 7] [14, 15]

In this example, since each LP counter is only 2 bits, the counterremains at the max value for the counter of 3 after 3 hops of a certainlevel of LCI or LQI has been noted.

For an example 5 hop route with the following LCI/LQI values (see TableA) would result in the corresponding LP value (see Table B):

TABLE A Hop LQI value LCI value 1 4 3 2 3 3 3 3 3 4 2 1 5 4 3

TABLE B

The fifth hop is the forth link with a level 3 LCI value, which isalready at the max counter value, so it is kept constant.

There is a configurable limit for TUd propagation. After the number ofhops exceeds the limit, the TUd is no longer propagated.

It is to be understood that this invention is not limited to thespecific devices, methods, conditions, or parameters described and/orshown herein, and that the terminology used herein is for the purpose ofdescribing particular embodiments by way of example only. Thus, theterminology is intended to be broadly construed and is not intended tobe limiting of the claimed invention. For example, as used in thespecification including the appended claims, the singular forms “a,”“an,” and “the” include the plural, the term “or” means “and/or,” andreference to a particular numerical value includes at least thatparticular value, unless the context clearly dictates otherwise. Inaddition, any methods described herein are not intended to be limited tothe sequence of steps described but can be carried out in othersequences, unless expressly stated otherwise herein.

While the invention has been described with reference to an exampleembodiment, it will be understood by those skilled in the art that avariety of modifications, additions and deletions are within the scopeof the invention, as defined by the following claims.

What is claimed is:
 1. A method for sending updates in a mobile ad hocnetwork, comprising: sending a full update every n^(th) update periodfrom each network node; and at update periods other than said n^(th)update period, each of said network nodes: (i) identifying which nodesin the network have corresponding Link Stability indicator (LSI) metricthat have changed by more than a predetermined threshold amount from animmediately preceding update period; and (ii) sending, as part of anupdate message, status information for the identified nodes, wherein theLink Stability Indicator (LSI) metric is computed asLSI_(ij)(t)=(w₁ΔLCI_(WMA)(t), w₂ΔLQI_(WMA)(t), w₃m_(i), w₄m_(j)) where,ΔLCI_(WMA)(t) is weighted moving average over time of a delta differenceof a link congestion indicator (LCI), ΔLQI_(WMA)(t) is weighted movingaverage over time of a delta difference of a link quality indicator(LQI), and m_(i) and m_(i) are mobility states.